1. Field of the Invention
This invention lies in the field of deep hole drilling by the rotary method. More particularly, it concerns a type of tool joint for drill pipe in which the transmission of torque from one joint of pipe to the other is by means of mating tongues and grooves in two sections of the tool joint, as in a jaw clutch, while the tensile strength of the joint is provided by a threaded collar which is screwed over the threads after the two halves of the tool joint are meshed.
Still, more particularly, this improved tool joint for drill pipe is concerned with large diameter drill pipe, and provides means for transmitting full torque of the drill pipe without transmitting it through the threads.
2. Description of the Prior Art
Currently available rotary shoulder tool joints for situations of extremely high drilling torques, are not satisfactory. Current tool joints rely on the face pressure between the mating surfaces of the threads to develop adequate frictional force to prevent the joint from making up tighter as drilling torque is transmitted through the joint. This is satisfactory for small diameter drill pipe, where the face contact area of the tool joint thread is large in relationship to the diameter of the drill pipe itself. These tool joints will develop torque transmitting characteristics equal to the torque capacity of the pipe body itself.
With the advent of large diameter borehole drilling, using drill pipe of 8 5/8 inches to 20 inches outside diameter, the problem of developing adequate torque transmission characteristics through the rotary shouldered tool joints becomes increasingly burdensome. Very high instantaneous drilling torques are common, which tightens each joint of drill pipe in the drill string, and on occasion has tightened joints to the point where the mating surfaces of the threads were literally welded together, and it was impossible to break the connections.